KITE WORK OF THE WEATHER BUREAU
Nebr., 29 per cent; Springfield, Ill., 21 per cent, and Fort Smith, Ark.,
12 per cent, the surface humidity being the higher, except at Fort
Smith. At thirteen out of the entire seventeen stations the differ
ence did not exceed 10 per cent, and at nine stations it was 5 per
cent or less.
For obvious reasons, as the altitude increased, the relative humid
ity decreased whenever the winds were from north to west, particu
larly from the northwest, and increased with winds from east to
south, particularly with those from the east. When the kite was in
or near clouds, the humidity would almost invariably rise, falling
again when the kite was freed from cloud influence.
Vapor pressures were expressed in percentages obtained by the
formula P, "p " representing the vapor pressure at any given altitude
and "po°"
that observed simultaneously at the earth's surface. The
mean thus obtained was 59 per cent, and there was a steady, though
by no means uniform, decrease with increase of altitude. The per
centage at 1,500 feet was 82 and at 8,000 feet 44. The decrease was
most rapid between 2,000 and 5,000 feet, where it averaged 9 per cent
for each 1,000 feet. The lowest percentage, 52, was found at Omaha,
Nebr., and the highest, 77, at Pierre, S. Dak.
A comparative statement of kite, balloon, and mountain observa
tions is given below. In determining these results the records of
1,123 kite ascensions were used. There were 4 balloon ascensions by
Hammon and 2 by Hazen. It is not known how many observations
were made by Hann.
Diminution of Vapor Pressurewith Altitude
Value of o for each respective 1,000 feet of altitude
p°
Character of observations.
1,500 2,000 3,000 4,000 5,000 6,000 7,000 8,000 Mean
feet. feet. feet. feet. feet. feet. feet. feet. feet.
K ite.................................................... 0.82 0.78 0.70 0.61 0.52 0.49 0.39 0.44 0.59
Balloon (Hammon)............ .......
.. ..... ..
0.96 0.96 0.87 0.68 0.44 0.59
..................
0.75
Balloon (Hazen)................................ 0.89 0.83 0.80 0.78 0.67 0.46 0.44
........
0.70
Balloon (Hann)................................... 0.84 0.80 0.66 0.61 0.60 0.54 0.41 0.37 0.60
Mountain (Hann)........................
0.83 0.81 0.80 0.66 0.61 0.58 0.55 0.47 0.66
Differences in wind direction were indicated by the changes in the
azimuths of the kites. These showed that, as an almost unvarying
rule, the general directions above and at the surface were practi-